My understanding was the gas burner provided more BTU than the electric element
The fridge is more efficient on gas. It will cool down faster with a flame than with the element.
The propane flame does provide higher BTU rating than the electric element BUT is less efficient in providing the needed BTUs in the correct place. The element is attached directly to the perk tube at the correct place for proper transfer of heat to ammonia solution where as the propane flame needs a flue baffle to disperse the heat and rest of heat flows out the chimney.
BTUs transferred to ammonia solution is about the same whether on propane or electric.